Flask



FIG. 1 is a top plan view of a flask showing my new design;

FIG. 2 is a front and rear view thereof;

FIG. 3 is a side elevational view thereof;

FIG. 4 is a perspective view thereof; and,

FIG. 5 is a bottom plan view thereof.

The broken line showing of the central region of the bottom surface is for environmental purposes only and forms no part of the claimed design. 

The ornamental design for a flask, as shown and described. 